1. Field of the Invention
The invention relates in general to a display module, and more particularly to a display module having an anisotropic conductive film (ACF) with improved adhesion performance.
2. Description of the Related Art
Liquid crystal displays (LCDs) are widely applied in various electrical products such as personal digital assistants (PDAs), notebook computers, digital cameras, digital camcorders, mobile telephones, computer monitors, liquid crystal televisions, and the like because the technology for manufacturing the LCDs is rapidly developed and the LCDs have the advantages of being light, thin, power-saving and radiation-free.
A liquid crystal display (LCD) module is assembled by the steps as follow. At first, two glass substrates are provided as a color filter (CF) substrate and a thin-film transistor (TFT) substrate respectively. Then, several driver integrated circuits (ICs) are mounted in a printed circuit board (PCB). The PCB is electrically connected to the TFT substrate after the CF substrate is bonded to the TFT substrate so that the LCD module is completed.
Ways of connecting driver ICs and a TFT substrate include tape auto bonding (TAB), tape carrier package (TCP), and chip-on glass (COG) technology. An anisotropic conductive film (ACF) is applied on several TCP leads of the TFT substrate prior to disposition of the driver ICs on the TCP leads, and then driver ICs are positioned on the TCP leads by heat head tools. So far, driver ICs are bonded with the TFT substrate. Further, TCPs are also bonded with the PCB by heat head tools.
As for COG technology, driver ICs are directly disposed on the TFT substrate and the COG process includes steps of using an ACF to be applied on several COG leads of the TFT substrate and using heat head tools to dispose driver ICs on the COG leads. Besides, the PCB connected with the TFT substrate is bonded with flexible printed circuits (FPCs) so that the TFT substrate is electrically connected with the PCB. An ACF is applied on FPC leads of the TFT substrate, and FPCs are disposed on the FPC leads by heat head tools.
A COG process is illustrated as below. FIG. 1 is a schematic diagram of a conventional LCD module. Referring to FIG. 1, a display module 10 at least has a glass substrate 11, and several driver ICs 12. The driver ICs 12 are disposed on the glass substrate 11 by a technique of chip-on-glass (COG). Before the driver ICs 12 are disposed, there are several COG leads disposed with respect to each of the driver ICs 12 on the glass substrate 11 in advance. Moreover, there are several flexible printed circuit (FPC) leads 13 separately disposed opposite to each of the driver ICs 12 on a marginal area of the glass substrate 11, such as FPC lead groups 13a, 13b, 13c, and 13d. Then, a FPC is further disposed on the FPC lead groups 13a, 13b, 13c, and 13d after a bar of anisotropic conductive film (ACF) is applied thereon.
However, the adhesion performance of an ACF to the glass substrate 11 at a space between two adjacent driver ICs or a space between two adjacent groups of leads, is poorer than areas on which driver ICs or leads are disposed, such as a space 15 between the driver IC 12a and the driver IC 12b, and a space 14 between the FPC lead group 13a and the FPC lead group 13b. Poor adhesion performance of the ACF causes emergence of glue residues on the heat head tools, which consequently influences the following disposition of FPCs. Moreover, TFT substrate is cracked by and the reliability of a total of the display module is deteriorated by such connection failures caused by poor adhesion performance of the ACF to the TFT substrate.